Changes in sugars and phenolics concentrations of Williams pear leaves during the growing season

Abstract

Leaves of Williams pear were collected during the growing season from May to October and the contents of sugars and phenolic compounds were analyzed by high-performance liquid chromatography method. Sorbitol was the major sugar (up to 83.8 g kg-1 DW), followed by sucrose (up to 22.1 g kg-1 DW). Concentrations of glucose and fructose were as high as 12.9 and 9.0 g kg-1 DW, respectively. Leaves contained up to 29 471.9 mg kg-1 DW of chlorogenic acid, followed in concentration by rutin (up to 6789.2 mg kg-1 DW), epicatechin (up to 7378.0 mg kg-1 DW), catechin (up to 3846.5 mg kg-1 DW), vanillic acid (up to 1832.1 mg kg-1 DW), syringic acid (up to 1123.5 mg kg-1 DW), caffeic acid (up to 122.5 mg kg-1 DW) and sinapic acid (up to 94.1 mg kg-1 DW). The significant differences in concentration of sorbitol, sucrose, glucose, and in all analyzed phenolics were observed during the growing season (six sampling dates). The lowest concentrations in the leaf were found at the beginning of the growing season in May and June. The highest contents of sugars were in October, with the exception of sorbitol. During the growing season, total phenolic content first increased, then declined. Chlorogenic acid, rutin and caffeic acid contents increased until July, vanillic acid and sinapic acid until August, and catechin, epicatechin and syringic acid until September. However, total phenolic content dropped by 50% from September to October. Key words: Pear leaves, sugars, phenolics, growing season